Patent literature 1 discloses a method and a structure for welding an accessory part to an outer wall surface of a fuel tank. The accessory part (a valve in patent literature 1) is made of a thermoplastic resin and includes: a housing having a hollow interior; and a flange extending from an end portion of the housing in a radially outward direction. The flange has a plurality of ribs formed thereon that project in a press direction.
The welding method carries out steps of: holding the accessory part on molds for molding a tank body; and molding the tank body by transferring a parison to the molds and, at the same time, pressing the flange and the plurality of ribs into the parison. When the flange and ribs are pressed into the parison, the flange and ribs melt due to the heat of the parison and whereby the accessory part is welded to an outer wall surface of the tank body. According to this conventional technique, due to the plurality of ribs, the accessory part can be welded even with heat of a relatively low-temperature (approximately 180° C.) parison.